Self-Purification Capacity And Physico-Chemical Assessment On A River Basin Pressured By Anthropogenic Influences: Example Of The Osam River, Bulgaria

Various anthropogenic impacts alter the structure and functioning of natural components, and the process of self-recovery in a damaged environment is more relevant than ever. Water quality worsens due to pollution with organic and inorganic chemical substances, and understanding the ability of aquatic streams to self-purify is a key challenge facing the scientific community. This article, dedicated to the Osam River (Bulgaria), provides knowledge on how eight physico- chemical elements change their concentrations from upper to lower reaches and to what extent the river manages to self- purify of pollutants. The paper is based on information concerning the values of DO 2 , N-NH 4 , N-NO 3 , N-NO 2 , N-tot, P-PO 4 , P-tot, and BOD 5 , recorded at four sampling sites from 2015 until 2021. Water quality is classified into one of three classes of physico-chemical status (excellent, good, or moderate) following the guidelines in Regulation H-4/14.09.2012 for surface water characterization. The self-purification coefficient of Tumas (α) is computed to determine the extent to which the river is able to rid itself of pollutants. The results indicate that water quality changes from upstream to downstream due to the inflow of untreated wastewater discharged from various sources and the ongoing self-purification processes. In the upper section, the river fails to get rid of phosphate pollution caused by households and industry, while in the lower sector, nitrate loading from agriculture is most disturbing. The current research focuses on the ability of rivers to restore their natural conditions under various anthropogenic impacts and points to the need for more effective control of unregulated discharges.